[PATCH] ieee80211: Fix A band channel count (resent)

The channel count for 802.11a is still not right. We better
compute it from the min and max channel numbers, rather than
hardcoding it.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>